Someone please give me a good explanation of the Schrodinger's Cat experiment please???

Question

I read it in a book "The Collapse of Chao" and saw it mentioned in the BBC Four show last night called "Atom", but I still don't really get what its about. Could anyone offer up a good explanation of the experiment and its results?

Answer 1

It's not a real experiment you can actually do - it's more of an illustration of the counter-intuitive nature of quantum physics. It goes like this:

You seal a cat in a box with a vial of poison gas. The vial is closed by some sort of lock attached to a piece of radioactive material (this is the important bit) which will open the vial if it detects a single particle being emitted by decomposition of the radioactive material, thus killing the cat.

Now it is a postulate of quantum physics that radioactive decay is fundamentally unpredictable. What's more, the theories say that in some sense quantum events (like radioactive decay) can be said to both happen and not happen *at the same time*.

Therefore, according to the experiment, until you open the box the cat is both dead *and* alive.

Answer 2

The schodinger's cat experiment demonstrates the measurement problem of quantum physics. While the cat is in the box the 'system' of the cat in the box with the cylinder of cyanide exists simultaneously in both states (ie cyanide cylinder open and cat dead and cyanide cylinder closed and cat alive) which is clearly nonsensical for a macroscopic system, but clever experiments show this to be the case for microscopic particles.

However, when the box is opened a 'measurement' occurs and the system can be seen to be in one state or the other.

A major problem for modern physics is that it appears that any system can evolve in a continuous manner in which a number of possible states apparently exist at the same time, but when 'measured' (a process for which there is no precise definition) only one state exists. So some ill defined measurement process causes a system to jump from a superposition of states evolving in a continuous manner to some discrete state, which continues to evolve linearly. Arguably the challenge for physics is to devise a consistent model that addresses both the continuous and discrete cases. The schrodingers cat experiment is simply a thought experiment which relates this to macroscopic objects to make it easier to visualise.

For more information on the measurement problem there are some very good answers to gumtrunk's question "Can you explain the Measurement Problem in science?"

Answer 3

The thought experiment is designed to show one of the basic problems of Quantum Mechanics. QM is all about probability, the cat is locked in the box and there is an equal probability that it is alive or dead. When you open the lid the probability collapses into one or the other state so by looking you have caused the outcome of the experiment.

There is a probability that an electron can be in one of a number of positions so to some extent it can be considered to be in all of these positions (superposition). When you measure the position it stops being in multiple positions and collapses into one. The act of measurement has affected the outcome of the experiment.

Please note, no actual cats were harmed while formulating this theory!

Answer 4

It was an exercise in logic used to explain quantum physics.
If you placed a cat in a sealed box with some cyanide gas, you can't tell if the cat is dead or alive unless you look. You cannot predict the condition of the cat at any given instant. And so with quantum physics you may be able to predict a probability but you can't know a particles actual position at any instant.
I always thought it was dumb, true but dumb.

Answer 5

Additionally, another major aspect of this is that the act of observing the phenom (here, the cat in the box) somehow changes the outcome.

Answer 6

Its a nonsense, but it helped explain why statistics were needed in quantum physics.
Unfortunately many rather tediously stupid physicists since will tell you that in the real world there are multiple possibilities for outcomes that exist simultaneously. (presumably simply because they cannot prove or see otherwise...a non-scientific argument if ever there was one!)
This is clearly not proved or even well illustrated by the "cat in the box".
(Some even suggest EVERY possibility gets played out in parallel universes - of course these people are all idiots)

Answer 7

Try going to
en.wikipedia.org/wiki/Schrodinger's_Cat